1. Field of the Invention
The present invention relates to a semiconductor laser, and more particularly to a semiconductor laser having a buried structure on a p-InP semiconductor substrate.
2. Description of the Related Art
With advancement of optical communication technologies, the fields to which such technologies are applied are rapidly expanding from the trunk transmission system to systems such as subscribers' system, a Local Area Network (LAN), and data links. Since such semiconductor lasers are used in a variety of environments and in a large quantity, they are required to satisfy a high environmental standard and yet they need be low in price. Thus, extensive researches are being made in this direction. A research which deserves attention relates to a semiconductor laser array formed on a p-InP substrate, which enables independent driving as in an optical interconnection light source used in computers, exchange machines, etc. (reported, for example, under the title "Low-threshold 1.3 .mu.m MQW laser array for optical interconnections" by Oka et al. in Technical Report of IEICE, OQE92-168, pages 13-18, (1993-02)). In such array, 10 to 12 semiconductor lasers are normally integrated so that it is important for the characteristics of such lasers to be uniform. In order to enhance the uniformity of the characteristics, it is necessary for a method to be available enabling fabrication of elements which excel in controllability and in uniformity of wafer surfaces. Thus, it has been hoped that a laser be realized by using a metal-organic vapor phase epitaxy (MOVPE) method which provides excellent characteristics as to controllability and uniformity.
Under such circumstances, all-MOCVD grown lasers on p-InP substrate have recently been reported under the title "LOW THRESHOLD FS-BH LASER ON p-InP SUBSTRATE GROWN BY ALL-MOCVD" by Y. Ohkura et al, in Electronics Letters, September 1992 Vol. 28, No. 19, pages 1844-1845.
However, in the buried structure in the semiconductor laser reported by Y. Ohkura et al, the current constriction structure takes a pnpn thyristor configuration called PBH (planar buried heterostructure) so that, although at room temperature of 30.degree. C., a low oscillation threshold current of 12 mA is obtained, a problem occurs at a high temperature of, for example, 85.degree. C. in that the oscillation threshold value abruptly rises due to an increase in the leakage current along with a decrease in the current blocking effects caused by the turn-on operation of the thyristor.